Dates for your Diary - IFALPA

More documents

Recommendations

Info

AP /FD TCAS: reduced stress RA reaction Since its inception, the Traffic Collision Avoidance System (TCAS) has significantly reduced the risk of mid air collisions; especially as the world’s airspace has become more congested and navigation systems increasingly accurate. However, the system in its present form is not without flaws. There is, for example, the problem of the crew reaction to TCAS Resolution Advisories (RA) which have, on occasion, led to become overreactions. To be honest, this is understandable, the surprise and stress that results from the RA can lead to a lack of communication with ATC, excessive aircraft attitude and airframe loading which have, in turn, led to injuries being sustained in the cabin. It is against this background that Airbus engineers have been studying methods to improve the response to TCAS Traffic Alerts (TA) and RAs. As a start point, the team led by Paule Botargues considered the way the TCAS system interfaces with the crew and the procedures employed to respond to RAs & TAs. To achieve this, the team considered the views express by pilots, data from human factors studies into the reaction to RAs as well as various recommendations from regulators. They found that the stress created by an RA and its accompa- nying aural cues is increased by the fact that the present procedure, which calls for the disconnection of the auto pilot and FD in order to follow the follow the red/green indications on the vertical speed indicator (VSI), is a non standard operation. This elevated stress contributes to the potential for overreaction which, in turn, can lead to the problems mentioned earlier as well as the generation of secondary RAs. An example of this type of event is the scenario where the crew of an aircraft Fig 1 Overreaction to an RA crew flies 3,500fpm advoidance profile compared with the correct value 1,500fpm increasing the risk of cabin discomfort or injuries as well as the possibility of a seondary RA being generated worsening the situation. The the VS is bang on the optimal avodance rate indicated by red/green zones on the VSI and all you jave to do is follow the FD. in level flight receives a ‘Climb’ RA which requires a VS of 1,500fpm (designed to deliver a maximum vertical displacement of 300ft 15seconds after RA initiation) instead a climb of 3,500fpm is initiated (generating higher positive G) and the vertical displacement of course is far greater leading especially in the RVSM environment to an elevated chance of a secondary RA calling for a descent (and the possibility of significant negative G during the pitch over). Another frequent scenario that was revealed by the study was the case where two aircraft (one in the climb) are brought into conflict by an incorrect response to an RA. In this case, aircraft 1 is in level flight at FL270 while aircraft 2 is in climb toward FL260 at July - August 2009
How does it work? AP & FD engaged: The AP/FD system engages TCAS mode in the autoflight computer and gives that system the necessary guidance to fly the optimum avoidance profile. AP Disengaged FD engaged: TCAS mode automatically engages as the new FD guidance system, the Pitch guidance, centres on a value which will deliver a vertical speed in the target zone (the green zone of the VSI) Both AP & FD are disengaged: The FD bars will automatically appear on the PFD with the TCAS guiding pitch as above. At any time the crew has the ability to disengage the AP and FDs in order to respond manually to the RA using the conventional TCAS procedure (flying out of the red) In case of a TA: The system is automatically armed in order to raise crew awareness that the TCAS mode will engage if the TA turns into an RA. In the case of corrective RAs: The TCAS longitudinal mode engages in order and delivers pitch guidance so that the target VS appears on the red/green zone boundary in order to minimise vertical speed deviation. As a result the following occurs in all modes: - TCAS longitudinal mode engages delivering pitch guidance to a vertical speed target +/-200fpm within the green zone with pitch authority increased by 0.3g. - All previously entered vertical profile modes are disabled with the exception of ALT which is designed to prevent undue altitude excursions. In a corrective RA a VS of 0fpm is considered as safe and is, therefore, never within the red zone and consequently the system will allow ALT capture. - Autothrust engages in the SPEED/MACH mode to ensure a safe speed throughout the manoeuvre -The lateral navigation modes remain unaffected In a Preventative RA: (i.e. and aural “MONITOR VS” alert): – Since the aircraft vertical speed is outside the red zone the requirement to follow the RA is to maintain a profile that remains outside the zone. Consequently: - The TCAS longitudinal mode engages to maintain the current safe vertical speed target. - All previously armed vertical speed modes are disabled with the exception of ALT mode. As with the corrective RA, a vertical speed of 0fpm will always fall outside of the red zone and therefore the system will allow ALT capture - Autothrust engages in the SPEED/MACH mode to ensure a safe speed throughout the manoeuvre - The lateral navigation modes remain unaffected Once clear of conflict: Vertical navigation is resumed as follows: - The AP/FD reverts to vertical speed mode with ALT mode re armed for the ATC cleared altitude and a smooth transition to towards the FCU target altitude. - If an ALT capture occurred during the course of the RA, once clear of conflict the AP/FD vertical mode reverts to ALT capture or ALT hold mode. - The lateral navigation mode remains unchanged. July - August 2009
Page 1 and 2: Airbus Extravaganza : A350 update,
Page 3 and 4: thrust as a percentage of the maxim
Page 6 and 7: A major contribution to aviation sa
Page 8 and 9: In a number of overrun incidents re
Page 10 and 11: The proof of the pudding As always,
Page 14 and 15: 3,000fpm. The system assuming a con
Page 16 and 17: advanced training on an accident in
Page 18 and 19: Running on empty: Fuel and airmansh
Page 20: around, that they would have had to

Dates for your Diary - IFALPA

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?